How HD Voice Works to Make Your Calls Sound Drastically Better

Will HD Voice really make calls clearer and put an end to yelling into our smartphones? Photo: Alex Washburn/Wired

Broken-up conversations, muffled voices and dropped calls will become a thing of the past if HD Voice lives up to its expectations. The major carriers have been teasing us with this vision of the future for years, and it looks like HD Voice is finally coming, for real.

AT&T announced Monday that its HD Voice will roll out later this year. It’s a part of the carrier’s voice-over-LTE strategy, which moves calls from AT&T’s older 3G network to its latest 4G LTE network. This followed T-Mobile’s recent announcement that it will deploy HD Voice on its iPhone 5 in mid-April, though the carrier has supported HD Voice since January. Sprint demoed its HD Voice feature last year and says it will roll out within months. That leaves Verizon, which so far has no plans to join the party until later this year or early next year.

But how exactly does HD Voice work? And is it marketing hype or something that will make smartphones finally excel as actual phones?

HD Voice is essentially wideband audio technology, something that long has been used for conference calling and VoIP apps. Instead of limiting a call frequency to between 300 Hz and 3.4 kHz, a wideband audio call transmits at a range of 50 Hz to 7 kHz, or higher. That’s much more in line with the human voice, which transmits audio between 75 Hz and 14 kHz.

HD Voice also takes in more audio samples per second than a standard call. Instead of 8,000 audio samples per second, HD Voice calls double that to 16,000. That way, you’re able to hear more details in a person’s voice during a call.

This technology isn’t particularly new. You’ve probably already experienced HD Voice while using an app like Skype, which supports these higher frequencies through its own audio codec, or while on a conference call. And many European carriers already support HD Voice over CDMA or GSM networks. It’s just that cellular phones and networks in the United States haven’t supported HD Voice. One reason might be because the feature does require more digital signal processing power. U.S. carriers have also been incredibly busy rolling out 4G networks, that it might not have made sense to support HD Voice over their legacy 3G networks.

Most of the latest smartphones now support HD Voice, including the iPhone 5, Samsung S III (and IV), HTC One, Nokia Lumia 920 and Sony Xperia Z. All of the phones have speakers and microphones that support wideband audio.

Now, all we need are carriers to actually enable HD Voice. They will do so by using a higher-quality speech codec called AMR-WB (Adaptive Multi-Rate Wideband). That codec doubles the frequency of the call, which means you’ll hear less muffled voices and be able to better distinguish between “s” and “f” sounds. VoLTE already supports AMR-WB, so it’s not very difficult for carriers like AT&T to enable HD Voice once calls have moved over to its LTE network.

It’s no gimmick. Once carriers actually support HD Voice, your call quality will drastically improve. Background noise should fade away while you’re chatting with your parents in a coffee shop. Your friend’s voices will sound more rich and life-like over the phone. And hopefully you’ll never again say, “Can you hear me now?”

There is a catch, however. HD Voice won’t be interoperable to start. That means both phones on the call must support HD Voice and share a carrier that supports HD Voice. That means if you have an iPhone 5 on AT&T and you’re calling someone with an iPhone 5 on Sprint, you won’t get an HD Voice-quality call. So don’t set your hopes too high, because not all your calls will suddenly get clearer.

Updated to clarify that T-Mobile has already launched HD Voice and will support HD Voice on its upcoming model of the iPhone 5.